Compact, simultaneous dual field of view through a common aperture

ABSTRACT

A compact, uniaxially-aligned series of lenses are shaped and coated to allow coaxial viewing of two different fields of view on the same focal-plane array by selecting a type of light. The selection can be, for example, by spectrum or polarization. Zonal coatings on the lens surfaces permit for a catadioptric narrow field-of-view light path. The lens assembly accomplishes simultaneous dual field-of-view in a durable package without respective motion of optical elements, without substantial gaps between the lenses, and at lower cost than other assemblies.

TECHNICAL FIELD

The present disclosure relates to optics, and in particular to compact,simultaneous dual field of view through a common aperture.

BACKGROUND

Many optical systems require a wide field of view, to search a largearea quickly, and a narrow field of view, to provide detailedinformation on an item of interest. Previous methods of achieving thisdual field-of-view (FOV) capability have involved complex andspace-intensive multi-element optical assemblies that are complex todesign and manufacture. Low-cost, space-limited applications previouslyhad not been able to incorporate dual-field-of-view capability.

Dual FOV systems provide both a wide field of view and a narrow, ormagnified, field of view of the same perspective. Typical examples ofnon-simultaneous dual FOV systems are the optical zoom lens assembliesfound in consumer video camera systems. Such systems work by moving lenscomponents with respect to one another to transition between minimum andmaximum FOV extents, termed “wide” and “zoom,” respectively. Suchimplementations involving moving lens components are bulky, expensive,and can be prone to damage, as from shock-induced misalignment ofoptical components, or failure of servomotors used to reposition theoptical elements with respect to each other. Such switched-FOV systemsare also unable to provide both fields of view simultaneously since theyrequire the movement of lenses to switch between fields of view. Otherdual FOV optical assemblies eliminate the requirement for moving lenses,but still involve substantial gaps between the optical components, andare thus similarly bulky, expensive, and fragile.

Systems employing what is known as “digital zoom,” which relies on imageprocessing techniques to digital create a narrow field of view from animage acquired from a wide field of view, can exhibit image degradationin the digitally enhanced narrow-field-of-view images, such aspixilation, enhancement algorithm artifacting, and noise. Digital zoomsystems are thus frequently inadequate for many applications.

SUMMARY

In one example, there is provided a lens assembly comprising at leastthree optical elements forming at least six optical surfaces configuredto simultaneously refract or reflect light from at least a first lightpath corresponding to a wide field of view and a second light pathcorresponding to a narrow field of view, the three optical elementsbeing arranged such that the first light path refractively transmitsthrough each of the surfaces, while the second light path transmitsthrough a first surface, a second surface, and a third surface,catadioptrically reflects off a fourth surface, reflects off the thirdsurface, transmits through the fourth surface and a fifth surface, andtransmits through a sixth surface.

In another example, there is provided an optical triplet comprisingthree lenses arranged uniaxially, the space between each lens being lessthan the width of any of the lenses, wherein the optical tripletsimultaneously outputs two different fields of view selectable by typeof light.

In another example, there is provided a uni-axial simultaneous dualfield-of-view lens assembly providing two different fields of view ofthe same perspective, a wide field of view and a narrow field of view,the assembly comprising at least three optical elements forming at leastsix optical surfaces configured to simultaneously refract or reflectlight from at least a first light path corresponding to a wide field ofview and a second light path corresponding to a narrow field of view,the three optical elements being arranged such that the first light pathrefractively transmits through each of the surfaces, while the secondlight path transmits through a first surface, a second surface, and athird surface, catadioptrically reflects off a fourth surface, reflectsoff the third surface, transmits through the fourth surface and a fifthsurface, and transmits through a sixth surface, in that order.

In another example, there is provided a dual field-of-view method forsimultaneously providing a wide field of view and a narrow field of viewof the same perspective, comprising transmitting light corresponding toa wide field of view along a first light path through at least threeoptical elements, and simultaneously transmitting light corresponding toa narrow field of view along a second light path through a first surfaceon one side of a first of the at least three optical elements, through asecond surface on an opposite side of the first of the at least threeoptical elements, and through a third surface on one side of a second ofthe at least three optical elements, catadioptrically reflecting thelight corresponding to the narrow field of view off a fourth surface onan opposite side of the second of the at least three optical elements,reflecting the light corresponding to the narrow field of view off thethird surface, transmitting the light corresponding to the narrow fieldof view through the fourth surface and through a fifth surface on oneside of a third of the at least three optical elements, and transmittingthe light corresponding to the narrow field of view through a sixthsurface on an opposite side of the third of the at least three opticalelements, in that order, so as to simultaneously provide a wide field ofview and a narrow field of view of the same perspective.

In another example, there is provided a lens assembly simultaneouslyproviding two different fields of view of the same perspective, theassembly comprising at least three uniaxially-arranged optical elementsforming at least six optical surfaces configured to simultaneouslyrefract or reflect light from at least a first light path correspondingto a wide field of view and a second light path corresponding to anarrow field of view, wherein a first optical element comprises a firstsurface coated in a central region with a first coating transmissive ofthe first light path and reflective of the second light path and coatedin an annular outer region with a second coating transmissive of thesecond light path and reflective of the first light path, and a secondsurface transmissive of both the first light path and the second lightpath, a second optical element comprises a third surface coated in acentral region with the first coating and not coated with the firstcoating in an annular outer region, and a fourth surface coated in anannular outer region with the first coating and not coated with thefirst coating in a central region, and a third optical element comprisesa fifth surface, and a sixth surface coated in a central region with thesecond coating and not coated with the second coating in an annularouter region.

In another example, there is provided a uni-axial simultaneous dualfield-of-view lens assembly providing two different fields of view ofthe same perspective, a wide field of view and a narrow field of view,the assembly comprising at least three optical elements forming at leastsix optical surfaces configured to simultaneously refract or reflectlight from at least a first light path corresponding to a wide field ofview and a second light path corresponding to a narrow field of view.The first optical element comprise a first surface coated in a centralregion with a first coating transmissive of the first light path andreflective of the second light path, and coated in an annular outerregion with a second coating transmissive of the second light path andreflective of the first light path. The first optical element furthercomprises a second surface coated in a third coating transmissive ofboth the first light path and the second light path. A second opticalelement comprises a third surface coated in a central region with thefirst coating and coated in an annular outer region with the thirdcoating, and a fourth surface coated in a central region with the thirdcoating and in an annular outer region with the first coating. A thirdoptical element comprises a fifth surface coated with the third coating,and a sixth surface coated in a central region with the second coatingand in an annular outer region with the third coating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a lens assembly providing refractivelytransmitted wide field-of-view light path.

FIG. 2 illustrates an example of a lens assembly providing acatadioptrically reflected narrow field-of-view light path.

FIG. 3 illustrates an example of a lens assembly simultaneously anduniaxially providing both a refractively transmitted wide field-of-viewlight path and a catadioptrically reflected narrow field-of-view lightpath.

FIG. 4 illustrates an example of zonally coated optical elements thatmay be used to provide the lens assembly of FIG. 3.

FIGS. 5a and 5b show an example field-of-view filter pattern for use inan airborne ground guidance with targeting application.

FIGS. 6a and 6b show an example field-of-view filter pattern for use inan automotive application.

DETAILED DESCRIPTION

A compact, uniaxially-aligned series of lenses are shaped and coated toallow coaxial viewing of two different fields of view on the samefocal-plane array by selecting a type of light. The selection can be,for example, by spectrum or polarization. The described lens assemblyaccomplishes dual FOV in a compact and low-cost package. No respectivemotion of optical elements is needed to achieve the dual field of view.The compact and static assembly makes the described assembly lesscomplex compared to prior solutions. Moreover, because it is compact andstatic, the provided assembly is more rugged and durable, and less proneto shock damage that can cause misalignment of optical elements. Theelimination of mechanical motion allows for more rapid automatic imageprocessing or human comprehension of output images.

Resultantly, the present disclosure provides simultaneous dual FOVsystems that do not involve moving lenses, do not require many opticalelements, do not occupy large volumes incurred by substantial air gapsbetween optical elements, and do not rely solely or primarily on“digital zoom” image enhancement techniques to provide imagemagnification.

Such features are useful in systems that need to switch from awide/acquisition field of view to a narrow/tracking field or to performprocessing from the two fields simultaneously. Example applicationsinclude autonomous road vehicle systems, field optics and viewingsystems, military and weapons systems, industrial visual inspection andquality-control systems, and aerial or underwater vehicle systems,whether unpiloted or piloted.

FIGS. 1-4 are illustrative of an example simultaneous dual field-of-viewsystem that does not require movement of optical elements and eliminatessubstantial gaps between the elements. FIG. 4 separates the opticalelements from each other for illustrative purposes only. In practice,there are no substantial gaps between the elements, as shown in FIGS.1-3. By “substantial gaps”, it is meant that each of the spaces betweeneach of all of the optical elements, including lenses, is less than thewidths of the optical elements themselves. For example, each of the gapdistances is less than 1125^(th) of the width of the optical elements.For example, less than 1150^(th). For example, less than 11100. Forexample, the gap distances are each less than 10 millimeters. Forexample, less than 2 millimeters. For example, less than 1 millimeter.For example, there is essentially no gap and the optical elements are inphysical contact with each other. Although FIGS. 1-3 do not show gapsbetween the elements 1, 2, 3, it will be appreciated that in practicethere may be some very minute gaps between the elements 1, 2, 3.

The system shown in FIGS. 1-4 comprises three lenses 1, 2, 3 in closeproximity to each other, as in an optical triplet. As shown best in FIG.4, each surface is coated in different zones to allow transmission orreflection of two different types of light, referred to herein as “lightpaths,” which can be discriminated either by spectrum or bypolarization. A “light path” herein comprises all of the optical raysthat make up one particular field of view, either wide or magnified(narrow). Thus, FIG. 1 shows a single light path, FIG. 2 shows a singlelight path, and FIG. 3 illustrates two light paths.

Thus it can be seen in FIGS. 1-3 that the system establishes twodistinct paths: one, an all-refractive wide field-of-view (WFOV) path 4,and two, a catadioptric narrow field of view (NFOV) path 6. The twopaths are transmitted simultaneously through the assembly comprising auniaxial optical triplet without substantial gaps between the opticalelements, at least some of the surfaces being coated in annularlyarranged zones to provide the desired transmission or reflectance of therays of the selectably distinct light paths.

In the illustrated example, light rays 8, 10 reflected from a viewingsubject enter the first optical element 1 from the left side of thedrawings and exit on the right side of the drawings, where they mayfocus on output planes 12, 14. Output planes 12, 14 may be one and thesame plane or may be slightly separated from each other in thelongitudinal direction. At the location of the output planes 12, 14 maybe any type of image sensor or medium for transducing or displaying theimage. For example, the illustrated lens assembly may be cooperativelycoupled to a charge coupled device (CCD) imaging sensor, a CMOSactive-pixel sensor, a stacked-photodiode photosite array sensor (e.g.,FOVEON X3), or any other appropriate imaging sensor.

FIG. 1 illustrates only the wide field-of-view (WFOV) light path 4,i.e., only those rays 8 that make up the WFOV image, as it passesthrough the three optical elements 1, 2, 3. The optical elements 1, 2, 3can be numbered in the order that light passes through them (e.g., firstlens 1, second lens 2, third lens 3) or can be named with reference totheir proximity to the imaging plane (e.g., outer lens 1, middle lens 2,inner lens 3). The WFOV light path 4 passes through all of thelenses—outer 1, then middle 2, then inner 3—refractively, with nosubstantial amount of light in the WFOV light path 4 reflected within orback out of the assembly. The curvatures and coatings of the surfaces ofthe lens elements are such that, in the illustrated example, a 30°half-field-of-view (½FOV) angle is produced at the output plane 12 onthe right side of FIG. 1.

FIG. 2 illustrates only the narrow field-of-view (NFOV) light path 6,i.e., only those rays 10 that make up the NFOV image, as it passesthrough the three optical elements 1, 2, 3. For purposes ofillustration, the outer annular portion of the leftmost optical element3 (i.e., the “third” or “inner” optical element 3) has been omitted fromthe drawing. The path of the NFOV light 6 is more complex than the pathof the WFOV light 4, since its interaction with the lens surfaces is notsimple refractive transmission, but instead depends on the zonalcoatings of the optical elements 1, 2, 3. Each lens element is said tohave two surfaces (the rim or edge surface(s) being ignored for thepurposes of the description, since they do not serve an optical functionhere). Thus, for three elements, there are six surfaces, which can benumbered from left to right (first through sixth) or named withreference to their proximity to the imaging plane (outer versus inner).As such, an “inner” or “outer” surface is not “inner” or “outer” withrespect to its internality or externality to the element, but ratherwith respect to the arrangement of elements. Alternatively, the surfacescan be termed according to their function in the “signal path” of thelight. Thus, for example, an outer surface (more proximal to a viewingsubject) can be termed an input surface and an inner surface (moreproximal to a detector assembly or imaging sensor) can be termed anoutput surface. In each of the following paragraphs, the direction oftravel of the NFOV light path 6, from “outer” to “inner” or from “input”to “output”, is from left to right on the drawing, except whereotherwise noted and due to reflection inside the lens assembly.

First, the NFOV light path 6 passes through a first surface 20 on oneside of the first optical element 1. Another way of saying this is thatthe NFOV light path 6 passes through the outside surface 20 of theoutside lens 1. Second, the NFOV light path 6 passes through a secondsurface 22 on the opposite side of the first optical element 1. Anotherway of saying this is that the NFOV light path 6 passes through theinside surface 22 of the outside lens 1. Third, the NFOV light path 6passes through a third surface 24 on one side of the second opticalelement 2. Another way of saying this is that the NFOV light path 6passes through the outside surface 24 of the middle lens 2.

Fourth, the NFOV light path 6 catadioptrically reflects off a fourthsurface 26 on an opposite side of the second optical element 2. Anotherway of saying this is that the NFOV light path 6 catadioptricallyreflects off the inner surface 26 of the middle lens 2. At this point,after the reflection, the direction of travel of the NFOV light path 6is from right to left on the drawing. Fifth, the NFOV light path 6reflects off the third surface 24. Another way of saying this is thatthe NFOV light path 6 reflects off the outer surface 24 of the middlelens 2. Again, the term “outer” is used with respect to the lens'sorientation and placement.

Sixth, the NFOV light path 6 transmits through the fourth surface 26.Another way of saying this is that the NFOV light path 6 transmitsthrough the inner surface 26 of the middle lens 2. Although the NFOVlight path previously reflected off of this surface 26, the transmissionin this step is possible because of the zonal coating 42, 44 on thefourth surface 26. The previous reflection was off an annular zone 44 ofthe surface whereas the transmission is through a differently coatedcentral zone 42 of the surface. Seventh, the NFOV light path 6 transmitsthrough a fifth surface 28 on one side of the third optical element 3.Another way of saying this is that the NFOV light path transmits throughthe outer surface 28 of the inner lens 3.

Eighth, the NFOV light path 6 transmits through a sixth surface 30 onthe opposite side of the third optical element 3. Another way of sayingthis is that the NFOV light path 6 transmits through the inner surface30 of the inner lens 3. Finally, the NFOV light path 6 can be resolvedon an output plane 14. The curvatures and coatings of the surfaces ofthe lens elements are such that, in the illustrated example, a 4.5°half-field-of-view (½FOV) angle is produced at the output plane 14 onthe right side of FIG. 2.

FIG. 3 illustrates, in the same drawing, the light paths of both theWFOV 4 and the NFOV 6 as they pass through the three optical elements 1,2, 3 of the system. Thus, in effect, FIG. 3 combines FIGS. 1 and 2.Particularly by comparing FIGS. 1 and 2, it can be noted especially fromthe rays 8, 10 entering the lens assembly on the left sides of FIGS. 1-3and the resolution of those rays on the imaging plane(s) on the rightsides of FIGS. 1-3 that the assembly provides a wide field of view and anarrow field of view of the same perspective. In the illustratedexample, there is a 6.7× difference in magnification between the WFOVand the NFOV. In FIGS. 1-3, rays of the WFOV light path 4 areillustrated with solid lines whereas rays of the NFOV light path 6 areillustrated with dashed lines.

A detector assembly (not shown) may be operatively coupled to theabove-described lens assembly to make the appropriate FOV selection(spectral, polarization, etc.) and to convert the optical energy to anelectronic signal that can, for example, be digitally processed,displayed, and/or used as input to vision systems. Such vision systemscan include autonomous or robotic systems, inspection systems, inventorysystems, flight navigation or control systems, targeting systems, orother vision-based or image-processing systems. If, for example,spectral selection is used in the lens assembly, a stacked diode type ofdetector array may be used to convert the optical output of the lens toelectronic signals corresponding to the two different field-of-viewimages. Such a sensor array detects one spectrum on its top layer andanother spectrum on its bottom layer. Under such circumstances it may bedesirable that the WFOV light path 4 and the NFOV light path 6 resolveon planes 12, 14 that are longitudinally spaces very slightly apart,such space being the distances between the selective layers of thesensor.

FIG. 4 illustrates the zonal placements of three different types ofcoatings on each of the three optical elements that make up the dual FOVlens system described above with reference to FIGS. 1-3. The coatingsare formulated such that they are reflective or transmissive dependingupon the type of light, where light can be classified into types basedon a variety of properties, for example spectrum or polarization. Thus,for example, where WFOV light is to be discriminated from NFOV light onthe basis of spectral characteristics, a particular coating can be, forexample, reflective of relatively high-frequency wavelengths buttransmissive of light of relatively low-frequency wavelengths, or bycontrast, can be transmissive of relatively high-frequency wavelengthsbut reflective of light of relatively low-frequency wavelengths.

Alternatively, where WFOV light is to be discriminated from NFOV lighton the basis of the orientation of propagation polarization, aparticular coating can be, for example, reflective of light that isplane-polarized in one direction but transmissive of light that isplane-polarized in an orthogonal direction. A detector assembly wouldthus achieve the task of separating the fields of view on the output endof the lens assembly. In order to perform the selection, the detectorassembly may make use of, for example, alternatively or in addition tothe sensor devices already mentioned, prisms, spinning filter wheels,alternating-orientation filters, louvered devices, filter mosaics,and/or digital micromirror devices (DMDs) to separate, distinguish, orselect light paths on the output end of the lens assembly.

In FIG. 4, then, a three-coating system provides the zonal coating thatcan implement the light path behavior described above with reference toFIGS. 1-3. A first coating, herein termed “coating A,” transmits lightof a first type and reflects light of a second type. A second coating,herein termed “coating B,” transmits light of a second type and reflectslight of a first type. A third coating, “coating C,” transmits lightboth of the first type and the second type. Again, the “type” cancorrespond to spectrum, polarization, or any other distinguishingproperty of the light.

The coatings are distinguished in FIG. 4 by differently oriented hashedmarkings. In the illustrated example, outer surface 20 of outer lens 1is coated with coating A in a central zone 32 but coated with coating Bin an annular outer zone 34. Inner surface 22 of outer lens 1 is coatedwith coating C on the entirety of the surface. Outer surface 24 ofmiddle lens 2 is coated with coating A in a central zone 38 but coatedwith coating C in an annular outer zone 40. Inner surface 26 of middlelens 2 is coated with coating C in a central zone 42 but coated withcoating A in an annular outer zone 44. Outer surface 28 of inner lens 3is coated with coating C on the entirety of the surface. Inner surface30 of inner lens 3 is coated with coating B in a central zone 48 butcoated with coating C in an annular outer zone 50.

Since coating C is transmissive of both types of light, corresponding tolight paths of both fields of view, in some examples there may be noactual coating used on the zones shown to be coated with coating C. Inother examples coating C may be a basic coating such as a clear coatingor a neutral density filter coating.

The use of the zonal coating accomplishes two things. First, it makesthe system very compact such that in one incarnation, the total pathlength is only 1.5 times the aperture of the narrow field of view.Second, the zonal coating keeps the system coaxial, which greatlyreduces manufacturing costs and increases boresight stability betweenthe two fields of view.

The interfaces between the zones can be “hard” or “soft,” which is tosay, the coatings may be formulated and deposited such that one zone mayend where another begins with no transition between the two zones (a“hard” interface) or the zones may blur into each other with some levelof gradation (a “soft” interface).

The coatings A, B, and C discussed above may be homogenous substancesdeposited onto the surfaces of the optical elements in their respectivezones, or may comprise layers of different substances. The materials andthicknesses of the coatings, i.e., the “recipes,” may be chosen fromamong any known coating recipes so long as they conform to thereflectance/transmission requirements for the different types of light,as set forth above.

The optical elements or lenses of the assembly may be made of anymaterials transparent to the particular wavelengths desired to be viewedusing the assembly. Such materials may be chosen from, for example,glass, crystal, plastic, acrylic (e.g., PMMA), polycarbonate,urethane-based pre-polymer, or thiourethane.

Although the individual zonally coated optical elements may be morecostly than standard optical elements, the simplicity of their mountinginto a single, short tube provides savings in assembly time. Moreover,the significantly lower weight, complexity, and volume provide largesavings in packaging. Consequently, the total manufactured cost of adual field-of-view system implementing the zonally coated opticaltriplet described herein may be a fraction of the cost of manufacturinga prior-art dual FOV system. Furthermore, the described system can beused in applications where the weight and volume of prior-art systemsrender them unusable. Especially in unmanned aerial vehicle (UAV) ormicro air vehicle (MAV) applications, for example, bulk and weight areprime considerations.

The shapes and sizes of the optical elements used in the described lensassembly can be tailored to the specific application. In the exampleillustrated in FIGS. 1-4, the first or outer or input optical element 1is a plano-convex lens with a concave central region 32 on the inputsurface 20. The second or middle or intermediate optical element 2 is aconcave-convex lens and may be a slightly negative meniscus lens. Thethird or inner or output optical element 3 is a concave-convex meniscuslens with a concave central region 48 on the output surface 30.

Although only three optical elements have been illustrated, a personskilled in the art will appreciate that the lens assembly may comprisemore than three optical elements. In the simplest arrangements havingmore than three optical elements, one or more additional opticalelements may be present on either side of the triplet, wherein theadditional element(s) either have no magnification effect or effect boththe WFOV and the NFOV in equivalent ways (e.g., widening both fields ofview, or narrowing both fields of view). Such optical elements may belenses, filters, or other components. Different arrangements based onthe same zonal coating principle could permit for differentlyproportioned dual fields of view or, conceivably, more than two fieldsof view (e.g., wide, narrow, extremely narrow). In such cases multipleadditional lenses could be used, appropriately coated to result in thedesired catadioptric reflection pattern necessary to produce themultiple fields of view.

By way of summarizing the above, the three optical elements 1, 2, 3 maybe joined as substantially a single optical piece such that mechanicalmotion between the elements is prohibited. The first optical element 1may mate with the second optical element 2 at their adjoining surfaces22, 24 and the second optical element 2 may mate with the third opticalelement 3 at their adjoining surfaces 26, 28 with essentially no gapsbetween the elements. That is to say, the second and third surfaces 22,24 may be mated such that there is substantially no gap between thefirst and second optical elements 1, 2, and the fourth and fifthsurfaces 26, 28 may be mated such that there is substantially no gapbetween the second and third optical elements 2, 3. The three opticalelements 1, 2, 3 may be joined as substantially a single optical piecesuch that mechanical motion between the elements is prohibited. Thisalso means that the two different fields of view may be provided withoutrequiring moving parts that move the three optical elements forming thesix optical surfaces with respect to each other.

Consequently, one or more filter elements may be configured to makelight in the WFOV light path distinct from light in the NFOV light pathby, for example, spectrum or by polarization. The total length of theNFOV light path 6 may be, for example, no more than 1.5 times theaperture of the narrow field of view. At least the first 20, third 24,fourth 36, and sixth 30 surfaces may be zonally coated to provide therefractive first light path 4 and the reflective second light path 6. Insome examples, there is at least a 6.7× difference between the WFOV andthe NFOV. In some examples, the three optical elements 1, 2, 3 formingthe six optical surfaces 20, 22, 24, 26, 28, 30 do not move with respectto each other, either axially or by translation of any of the elements.

Different applications may call for different filter patterns at theoutput of the lens assembly, as processed by, for example, theaforementioned detector assembly or imaging sensor. FIGS. 5-6demonstrate example field-of-view filter patterns for use in differentapplications. FIGS. 5a-5b show an example of a centered ellipticalfilter pattern suitable for providing airborne ground guidance withtargeting when the lens assembly is provided in an aerial vehicle. TheWFOV 60 is available for ground feature guidance while the NFOV 62 isavailable for targeting. In the illustrated example, a distant enemyvehicle is shown magnified in circularly filtered NFOV 62 while thewider landscape, including features useful for vision-based navigation,is visible in WFOV 60. Whether filtered by the illustrated pattern ornot, the WFOV can be provided to a ground feature guidance system in theaerial vehicle while the NFOV can be provided to a targeting system.

Similarly, FIGS. 6a and 6b show an example of a rectangular filterpattern suitable for use in a driver-assist or driverless automotiveapplication when the lens assembly is provided in a road vehicle. Forexample, the car's lane detection systems can use the WFOV 70 while thecar's obstruction detection systems can use the NFOV 72. In theillustrated example, a distant deer that threatens an imminent collisionis shown magnified in rectangularly filtered NFOV 72 while the widerlandscape, including road edges and markers, are visible in WFOV 70.

The described examples provide uniaxial dual FOV without requiring axialor translation movement of the lenses. Systems with axial translation,such as camcorder zoom lenses, move the lens elements with respect toeach other along the same path that the light travels. Systems withtranslation movement bring lenses or lens portions into and out of thepath of light by laterally translating the optical elements.

What have been described above are examples of the present invention. Itis, of course, not possible to describe every conceivable combination ofcomponents or methodologies for purposes of describing the presentinvention, but one of ordinary skill in the art will recognize that manyfurther combinations and permutations of the present invention arepossible. Accordingly, the present invention is intended to embrace allsuch alterations, modifications and variations that fall within thespirit and scope of the appended claims.

I claim:
 1. A lens assembly comprising: at least three optical elements forming at least six optical surfaces configured to simultaneously refract or reflect light from at least a first light path corresponding to a wide field of view and a second light path corresponding to a narrow field of view to provide simultaneous dual fields of view, the at least three optical elements being arranged such that the first light path refractively transmits through each of the at least six optical surfaces, while the second light path transmits through a first surface of the at least six optical surfaces, a second surface of the at least six optical surfaces, and a third surface of the at least six optical surfaces, catadioptrically reflects off a fourth surface of the at least six optical surfaces, reflects off the third surface, transmits through the fourth surface and a fifth surface of the at least six optical surfaces, and transmits through a sixth surface of the at least six optical surfaces.
 2. The lens assembly of claim 1, wherein at least three of the at least three optical elements are joined as substantially a single optical piece such that mechanical motion between the three of the at least three optical elements is prohibited.
 3. The lens assembly of claim 2, wherein a first optical element of the at least three optical elements mates with a second optical element of the at least three optical elements at respective surfaces adjoining the first and second optical elements and the second optical element mates with a third optical element of the at least three optical elements at respective surfaces adjoining the second and third optical elements with essentially no gaps between the first and second optical elements and essentially no gaps between the second and third optical elements.
 4. The lens assembly of claim 1, further comprising one or more filter elements configured to make light in the first light path distinct from light in the second light path by spectrum.
 5. The lens assembly of claim 1, further comprising one or more filter elements configured to make light in the first light path distinct from light in the second light path by polarization.
 6. The lens assembly of claim 1, wherein the total length of the second light path is no more than 1.5 times the aperture of the narrow field of view.
 7. The lens assembly of claim 1, wherein at least the first, third, fourth, and sixth surfaces are zonally coated to provide the refractive first light path and the reflective second light path.
 8. The lens assembly of claim 1, wherein there is at least a 6.7× difference between the wide field of view and the narrow field of view.
 9. The lens assembly of claim 1, wherein at least three of the at least three optical elements forming the six optical surfaces do not move with respect to each other, either axially or by translation of any of the elements.
 10. The lens assembly of claim 1, wherein three of the at least three optical elements form an optical triplet comprising three lenses arranged uniaxially, the space between each lens being less than the width of any of the lenses.
 11. The lens assembly of claim 10, wherein the space between each lens is less than 10 millimeters.
 12. The lens assembly of claim 10 coupled to an imaging sensor and provided in a road vehicle having a lane detection system and an obstruction detection system, wherein the imaging sensor resolves the two different fields of view as a wide field of view and a narrow field of view, and the wide field of view is provided to the lane detection system while the narrow field of view is simultaneously provided to the obstruction detection system.
 13. The lens assembly of claim 10 coupled to an imaging sensor and provided in an aerial vehicle having a ground feature guidance system and a targeting system, wherein the imaging sensor resolves the two different fields of view as a wide field of view and a narrow field of view, and the wide field of view is provided to the ground feature guidance system while the narrow field of view is simultaneously provided to the targeting system.
 14. The lens assembly of claim 10, wherein a first optical element of the at least three optical elements comprises: the first surface, coated in a central region of the first surface with a first coating transmissive of the first light path and reflective of the second light path and coated in an annular outer region of the first surface with a second coating transmissive of the second light path and reflective of the first light path, and the second surface, transmissive of both the first light path and the second light path.
 15. The lens assembly of claim 14, wherein a second optical element of the at least three optical elements comprises: the third surface coated in a central region of the third surface with the first coating and not coated with the first coating in an annular outer region of the third surface, and the fourth surface coated in an annular outer region of the fourth surface with the first coating and not coated with the first coating in a central region of the fourth surface.
 16. The lens assembly of claim 15, wherein a third optical element of the at least three optical elements comprises: the fifth surface, and the sixth surface coated in a central region of the sixth surface with the second coating and not coated with the second coating in an annular outer region of the sixth surface.
 17. The lens assembly of claim 16, wherein the first optical element is mated with the second optical element at the interface between the second and third surfaces, which adjoin such that there are essentially no gaps between them, and wherein the second optical element is mated with the third optical element at the interface between the fourth and fifth surfaces, which adjoin such that there are essentially no gaps between them.
 18. The lens assembly of claim 16, wherein the total length of the second light path is no more than 1.5 times the aperture of the narrow field of view.
 19. The lens assembly of claim 18, wherein there is at least a 6.7× difference between the wide field of view and the narrow field of view.
 20. The lens assembly of claim 19, coupled to an imaging sensor and provided in a vehicle. 